ReviewPsychobiotics: A Novel Class of Psychotropic
Section snippets
Probiotics
The term probiotic is derived from the Greek meaning for life and the first formal description of a probiotic was provided by Metchnikoff in 1908, based on his observation that individuals who lived in a certain region of Bulgaria had a longer life span than those in other parts of the country, a fact that he related to the regular consumption of a fermented milk product (5). Probiotics are currently defined as a live organism that, when ingested in adequate amounts, exerts a health benefit (6)
Gut Microbiota
The gut microbiota is a complex metabolic ecosystem and when adults ingest probiotics, such bacteria usually transit the gut or transiently colonize rather than becoming a permanent feature (18). The adult gut is inhabited by 1013 to 1014 microorganisms, a figure thought to be at least 10 times greater than the number of human cells in our bodies with 150 times as many genes as our genome 19, 20. The estimated species number varies greatly but it is generally accepted that the human microbiome
Microbiota, Immunity, and Depression
The development of the intestinal immune system is largely dependent upon exposure to microorganisms. The GF paradigm is based on the fact that the uterine environment is sterile during prenatal development and with surgical delivery replacing the normal vaginal delivery, the opportunity for postnatal colonization of the gut is eliminated once animals are maintained in a sterile environment. In GF animals, which are almost without immune activity, association with certain selected
Microbiota and Hypothalamic-Pituitary-Adrenal Axis
The use of GF animals has provided one of the most significant insights into the role of the microbiota in regulating the development of the hypothalamic-pituitary-adrenal (HPA) axis. Subsequent comparison with their conventionally colonized counterparts allows inferences to be drawn regarding the morphological and physiological parameters that may be under the influence of the developing microbiota. However, in the absence of the resident enteric microbiota, key members of the TLR family have
Psychobiotics and Neurotransmission
Over the past 25 years, well-tolerated antidepressants have emerged that largely target 5-HT and/or norepinephrine (NE). However, not all patients respond to antidepressants and some patients are averse to pharmacologic interventions. From a biological perspective, it is known that depressed patients frequently have HPA alterations, such as elevated cortisol levels in plasma, elevated corticotropin-releasing hormone levels in the cerebrospinal fluid, and a failure to suppress cortisol in
Clinical Studies
Irritable bowel syndrome is a disorder of the brain-gut axis and is associated with a high degree of comorbid depression and anxiety (76). Several well-designed studies of probiotics have been conducted in this disorder 77, 78. O’Mahony et al. (77) carried out a parallel group, placebo-controlled study comparing B. infantis and L. salivarius. The latter had little impact on symptoms, while B. infantis resulted in significant improvement. This therapeutic benefit occurred within the context of a
Whither Psychobiotics?
There are sufficient preclinical data to support the view that clinical studies with probiotics in depression are worth conducting. It is equally clear that not all probiotics are the same and most do not have psychobiotic potential. Numerous putative probiotics studied in our laboratory were found to have no demonstrable impact on behavior. To detect psychobiotics, we would favor probiotic strains that preclinically have shown behavioral effects, are delivery vehicles for neuroactive
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